1. Field of the Disclosure
The present disclosure generally relates to the fabrication of microstructures, such as integrated circuits, and, more particularly, to implanting ion species by means of ion implantation tools required for producing well-defined doped regions in specified material regions and/or treating specific device regions.
2. Description of the Related Art
The fabrication of complex microstructures, such as sophisticated integrated circuits, requires that a large number of individual process steps be performed to finally obtain the required functionality of the microstructure. Especially during the fabrication of integrated circuits, the conductivity of specific areas has to be adapted to design requirements and also, frequently, the state of materials in specified device regions may have to be modified, at least temporarily, for instance with respect to crystalline structure and the like. For instance, the conductivity of a semiconductor region may be adapted, for example, increased in a well-defined manner, by introducing specific impurities, which are also referred to as dopants, and placing some or preferably most of these impurities at lattice sites of the semiconductor crystal. In this way, so-called PN junctions may be formed that are essential for obtaining a transistor function, since transistors represent the active elements, i.e., elements providing current or voltage amplification, which are required for manufacturing electronic circuits. In other cases, the modification of the crystalline state or the adaptation of the material characteristics, for instance in view of etch behavior, internal stress levels of materials and the like, may be required, permanently or temporarily, in order to enhance device performance and/or provide a more efficient process flow. For example, at some stages of the manufacturing flow of complex integrated devices, a substantially amorphous state of a portion of drain and source regions may be advantageous for a variety of reasons.
In modern integrated circuits, millions of transistor elements, such as field effect transistors, are typically provided on a single die, wherein, in turn, a plurality of dies are provided on a single substrate. As the critical dimensions of certain circuit elements, such as field effect transistors, have now reached 0.05 μm and even less, it is of great importance to correspondingly “fine-tune” the profile of doped regions in the lateral direction, with respect to a substrate, as well as in the depth direction. In this respect, ion implantation has been proven to be a viable technique for introducing a great variety of species into materials of microstructure devices and therefore ion implantation is currently the preferred method of introducing dopants into specified device regions, due to the ability to precisely control the number of implanted dopant atoms into substrates with a repeatability and uniformity of better than ±1%. Moreover, impurities that are introduced by ion implantation have a significantly lower lateral distribution when compared to conventional diffusion dopant processes. Since ion implantation is typically a room temperature process, the lateral profiling of a doped or otherwise implanted region may, in many cases, be conveniently achieved by providing a correspondingly patterned photoresist mask layer. These characteristics may render ion implantation, currently and in the near future, the preferred technique to produce doped regions in a semiconductor device and also make ion implantation an attractive technique for appropriately modifying material characteristics in view of effects, such as local strain relaxation, local amorphization of initially crystalline regions, locally adapting etch rates and the like.
Implantation of desired species is accomplished by ion implantation tools, which represent extremely complex machines requiring continuous monitoring of the machine characteristics and the machine status to achieve high efficiency and machine utilization. In particular, maintenance activities may have to be performed on a regular basis in order to re-condition the state of certain components of the implanter tools that suffer from increased wear during the operation of the implanter, as will be described in more detail with reference to FIG. 1.
FIG. 1 illustrates a schematic view of an ion implantation tool 100 comprising an ion source 101 having an input 102 that is connected to respective precursor source gases (not shown), such as boron fluoride (BF3), phosphorous hydride (PH3), arsenic hydride (AsH3), carbon fluoride (CF4) and the like, from which an appropriate ion species may be created in the ion source 101. The ion source 101 may be configured to establish a plasma atmosphere and to pre-accelerate charged particles into a beam pipe schematically depicted as 103. Downstream of the ion source 101, an accelerator tube 104 is arranged that is dimensioned to accelerate ions with a specified voltage, which may typically range from zero to approximately 200 keV for a typical medium current implanter and may range to several hundred keVs or even to 1 MeV or more in high-energy implanters. Downstream from the accelerator tube 104, a beam shaping element 105, such as a quadruple magnet, may be arranged, followed by a deflector magnet 106. Downstream of the deflector magnet 106 is disposed an analyzing aperture, for instance in the form of a slit 107, the dimensions of which substantially determine an energy spread of the ion beam. Thereafter, a further beam shaping element, such as a quadruple magnet 108, may be provided downstream of the analyzing slit 107.
Furthermore, a substrate holder 109 is located in the vicinity of the end of the beam line 103, wherein, typically, the substrate holder 109 may be provided in the form of a plate enabling the receipt of one or more substrates 110. The plate 109 is typically connected to a drive assembly (not shown) that enables movement of the substrate holder 109 in the transverse direction (as indicated by the arrows depicted in FIG. 1) and also allows control of the tilt angle, at least in two planes, at which the ion beam hits the substrate 110. For convenience, corresponding well-established means for controlling and adjusting the tilt angle are not shown. Moreover, a first ion beam detector 111 may be provided, for instance, embodied by a plurality of Faraday cups that are connected with respective current measurement devices. Furthermore, a second ion beam detector 112 may be provided as a so-called traveling Faraday cup that is laterally movable to determine the shape of an ion beam and/or to shade respective Faraday cups during the measurement of specific beam characteristics, such as the angle of incidence.
During the operation of the ion implantation tool 100, an appropriate precursor gas is supplied by the inlet 102 to the ion source 101, in which an arc discharge may be established to produce a plasma ambient for generating ions of atoms included in the precursor gases. Thus, an appropriate voltage may have to be applied to the gas ambient to ignite and maintain a plasma, thereby producing accelerated particles, which may also come into contact with the chamber walls and other internal components, such as tungsten wires and the like. The ions within the ion source may be accelerated into the beam line 103 by means of a pre-accelerator means. Typically, a plurality of ions having different charge states may be supplied by the ion source 101 during the creation of a plasma ambient and may thus be introduced into the acceleration tube 104. Typically, a preselection of the type of ions and of the respective charge states may be accomplished within the ion source 101 by a corresponding deflector magnet (not shown). Thereafter, the ions pass the accelerator tube 104 and gain speed in accordance with the applied acceleration voltage, the charge states of the respective ion and its corresponding mass. Hence, the acceleration tube 104 comprises electrodes for applying the required high voltage at defined positions of the tube 104, wherein insulators provide electric insulation of the electrodes in order to suppress high voltage breakthroughs, which may result in beam instabilities and the like. By means of the quadruple magnet 105, the ion beam may be focused in one dimension and may be correspondingly defocused in the perpendicular dimension and the correspondingly shaped beam is directed to the deflector magnet 106. The current generating the magnetic field of the deflector magnet 106 is controlled so as to deflect the trajectory of desired ion species having a desired charge state to the opening of the analyzing slit 107. Ions of differing mass and/or charge state will typically hit the analyzer 107 without passing through the slit. Thus, the ions in the beam passing the analyzer 107 have a well-defined mass and an energy distribution defined by the slit size.
It should be noted that, in some ion implantation tools, the deflecting magnet 106 and the analyzer 107 are configured such that the ion beam passing through the analyzer 107 may be scanned in a transverse direction so as to cover the whole area of a substrate or at least a significant portion thereof, since the dimension of the beam shape, i.e., the size of the beam spot, is usually, depending on the energy of the ion beam, significantly less than the area of a substrate to be processed. Next, the beam passing through the analyzer 107 may be further shaped by the quadruple magnet 108 so that, in combination with the quadruple magnet 105, a desired beam shape may be obtained that finally impinges on the substrate 110 to cause the desired effect, such as positioning a dopant at a desired depth and with a desired concentration and the like.
During the implantation processes, however, the ionization of the source gas in the chamber 101 may result in an increased interaction with chamber walls and other components, as previously discussed, thereby increasingly sputtering off material from these components, which may therefore also be ionized and accelerated into the beam line 104 and to any component downstream from the beam line 104. These materials may “condensate” on specific components of the implantation tool 100, wherein, in particular, the sputtering off of conductive materials, such as tungsten, may result in the deposition of this conductive material at sensitive areas, such as insulating materials, which may thus increasingly accumulate and reduce the insulating capabilities thereof, finally resulting in additional high voltage discharges between neighboring high voltage regions, thereby contributing to significant beam instabilities. Moreover, because of the increasing accumulation of unwanted materials, such as tungsten and the like, modification of the beam characteristics may be observed, even prior to actually causing additional breakdown events between adjacent high voltage components, thereby also contributing to process non-uniformity. For these reasons, cleaning processes for conditioning the implantation tool 100 have to be performed on a regular basis, which may be accomplished by generating argon or xenon ion beams during respective cleaning periods of the implantation tool.
For example, implantation processes performed during the manufacturing of semiconductor devices that are performed on the basis of boron fluoride (BF3) as a source material, or boron ions, boron fluoride ions, or fluorine ions, as well as implantation processes performed on the basis of carbon fluoride as a source material for creating carbon ions, carbon fluoride ions and fluoride ions, are well known to cause a pronounced sputtering effect in the ion source 101, which may thus result in a subsequent enhanced condensation of these materials along relevant portions of the beam line 105. Also, other implantation processes, for instance using phosphorous hydride (PH3) and arsenic hydride (AsH3), which may be used for introducing dopant species for forming drain and source areas, may also result in an accumulation of material after several hours of operating the implantation tool 100.
Consequently, preventive maintenance activities may be necessary on a regular basis to recondition the beam line to provide enhanced process uniformity during the operation of the implantation tool for processing actual products. However, the required conditioning of the beam line may result in reduced throughput and thus increased production cost, as typically a higher number of implantation tools may have to be provided in a semiconductor facility for a given desired overall output.
The present disclosure is directed to various methods that may avoid, or at least reduce, the effects of one or more of the problems identified above.